High pressure plastic injection molding machine clamps



Sept. 24, 1957 A; J. ROGER 2,307,050

HIGH PRESSURE PLASTIC INJECTION MOLDING MACHINE CLAMPS Original Filed Dec. 19, 1949 ALBERT J. ROGER INVENTOR.

United States Patent. Ice.

HIGH. PRESSURE PLASTIC INJECYPIGNIMOBDING GLA MIS? i Albert'J. Roger, Oakland; (-Z'alifi, assignor to CrownMachine&1To0lC0mpany,' FortWortli, ,Tex., a corporation of Texas Claims. (Cl. 18- -30) This inventionrelates-to clampsfor plastic molding machines of theinjection type: g

It is-oneof theobjectsofthisinventiorr toproyide' a mold clamp which successfully; accommodates "molding dies of a type havingcavities-which-are'relativelydeep and 'which have dimensions such that during injection" of the plastic very largemoldseparatingforcesidevelop'.

It is another object of this invention. to provide: a clamp which continuously withstands." the high separating'forcesinoidenttoinjection; and which'itself'is capable of developingsufiicient' force to separate' the mold? parts from the article after the article has solidified in the mold It is a further ob'ject of" the invention to'providefor the etficient, safe, and' autOmatio sequential operation of thevarious functional elements of myclamp:

Additional objects andadvantages of' my invention will. become: evident from a consideration-- of 'the follow ing specification: and; accompanying drawing;- in which} The drawing: issa. diagram illustrating. the essential details; ofiai clamp" according to the invention;

Like elements are designated by like characters throughout thespecification and: drawings;

Inther drawing Ia. vertical: type cla'rn'p is illustratedito comprise a.rigid; base: a and an. upper: platen: 12 which arejoined together rigidly: by a plurality; as four"; of vertical and: parallel strain rods l4z Platen1'2-is ad justablabetweenpairs of nuts 16': on ther-rodsrleb: The rods 14. may; be extended: in: aconventional: manner: for securementto a header plate (-no'eshown);.Suclrzheadr plate: serving tosmaintain the parallel: alignment iofr'strain rods 14 when platen 12 is loosened! fonadjustmentr.

The upperplatenlZ-has secured=thereto one part. 18 of. atmolddie; A movable platen 20 is mountedxtotslide on rods 14 toward and. away from platen 12"- andhas securedthereon. a second part 1-9 of. the-mold: die. A: fluid actuated motor 22 comprising. a piston 24Q-inr a cylinder. 26' actuates a. piston rod -28 whichrod supports and is secured-as by threading .in theplaten 20iand trans.-. mits motion from piston.2'4"thereto.-. Thepistom M-has; a long stroke in. cylinder 26; the vertical 6Xt11lLOfsWhiGll is designed to be sufficient to permit the. insertion of. mold parts 18. and 19'of' a wide rangeofverticaldirnenr. sions. The diameter of piston 24 and cylinder. 26 is small; being only. large enough to supply adequate; thrustand; power to rapidly move. the mold'part 19 from the fully openposition' shown to a position con.. tacting or nearly contacting the mold part 18.

Thecylinder 22 is secured and pressure sealed to a" piston 30 WhlCh'iS- movable vertically in the direction of motion ofpiston 24. Piston-30-is receivedin a cylinder 32: provided by base 10 which' base further provides acylinder; head 341 opposed to piston 30. During the vertical movements of platen 20 under compulsionof piston-24;,the thrust of platen 20 is .tran smitted via pistonz 24= and the-fiuidin cy1inderf26 to: the-head of 'piston 30l whichxpistonzheadgengagesrthe; surface=36 ofithe oylinder head 34 and receives support therefrom.

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2,807,050 Fatentdsepr. 24, 1957 The platen 20 provides; on the l'owerface thereof and concentric .ofpiston'rod 28, an annular shoulderedbearing 38 on.which1there is'journalled a blocking plate 40 having, preferably, three holes 42'spacedat onehundred and twenty degree intervals therein on..a--circle.of common radius from the center. of journal 38. The. plate 40 is permitted a slight vertical displacement between the shoulder. of bearing 38 and the bottom flat face 44 of platen. 20:

The upper surface of piston 30' carries, in addition to motor 22, three thrust rods.46' ofasize to pass through openings 42"in'blocking,disc 40and positionedwith their axes parallel to. the axes of'thestrain rods 14' and. at onehundred. and twenty degree intervals about'the axis of journal138, the. radius of their center lines from the axisof'journal 38. being jthe same as that for: the location of"p assages 42'. The thrustrods 46'are removably positioned'by foot sockets 48 secured.to piston; 30. The platen 20,.provides passages 50 in registry. with. sockets 48;,into,. or through; whichv the. rods -46i'projectih the position shown in the drawing;

The apparatus'described to this point is operable. as follows: a

From the position shown,-.upon ad'misiOnofi'hydraw lie. fl'uid. under.v adequately, sustained pressure beneath piston 24;.the platen 2'0' and 'mo1dlpart-l9. are raised and heldito.contactmoldpart 18,.the contact stopping..fur.- ther. movement. When: so. moved. the..uppen ends of rods 46 are free. ofh'oles 42inthe..b1ocliii1g.plate.. 40. Plate 40" is. now rotated.- so. that-holes, 42.. are. out. of registry withrods. 46. andisov that thebody ofthebloclcing plate is interposed. between. holes- 50; of. platen 20. andlth'e ends ofirods 46: Having. so..positioned. blocking plate. 40,. thev pressure.- in: cylinder. 26. may .be released; though. itineed. not. be.v If. thetpressure. in cylinder-.26 is released the platen 20 rests..on-thrust-.rods 46. through the plate. 40,-. and piston. 24 .is idle..

To.v cause. the. interfaces of thetmoldl parts. 18 and. 19- to engage eachrother. with great force;.enough..sufficient to.- prevent. flash. of plastic material therebetween,.- fluid under pressure is. admitted. into cylinder 32.- under piston 30.. Avery. slight movement, if any, occurs upwardly; and..the. gross thrust ()Ihthe, die interfaces isisubstantiallyy equallto theunit pressure in cylinder 32.=multipliedby the.area of piston.-30.-v Thus, even thoughthe same-value of pressure. be used. under piston 30- as. was previously; used under. piston 24, the: gross upward: thrust issgreaterr than that of which piston 24 is capable in the-ratiosofl the. areasof. the twotpistons. I

- ThecOrnbinod weights of the. moving; parts includingdie 19,-,platen-20; and-plate 40 does not usual1y=exceedfivetons and the thrust required tozholdthe diespart'si 1'8: and 19. closed-oftenexceeds-five hundred tons: Accord ingly-,1the.'piston 24'- may" be made: very small? in: thrust area and the.- unit pressure applied thereto: may also. be? small; T-heunit:pressurerapplied.to piston 30ris1SeleCted. inaccordance with that tobe resisted from the mold' itself, and often is several thousands of pounds :per. square: inch Thestrain rods 14-and the. thrust;rods;46:arc; of; course,:.designed to withstand: tension and. compression.

stresses corresponding .to these. values of. clamping pressures.

Itwilll be notedthat the rods 46.-are.-so selected for. length that their upper ends just clear. the lOWCIrffiCSLOf. plate 40' whenthe die parts are in contact. Therefore, when plate .40 is interposed to block. movement of platen 2'0.- downwardly, the only relative movement of'piston30 to" itscylihder' that can ensue is that. necessary to force plate40ag ainst platen 20to compress the rods 46'and.- other parts interposed between piston 3'0"andplaten 12; and tow stretch rods 14 sufficiently to" develop" the total tensile=- force required to resist the compression of the piston thrust. These distances sum up to a few thou- I sandths of an inch. Accordingly, the amount of liquid required to displace piston 30 enough to effect the required thrust is small.

The injector and molds are provided with the conventional nozzle and sprue apparatus including a nozzle 50 and seat 52. The nozzle 50 is applied when the piston 30 has been fully actuated to clamp the mold parts, and the charge of fluid plastic material is forced into die 18 and 19, thereby developing a large thrust tending to part the mold parts 18 and 19 by adding further to the stretch in the strain rods 14. If the die parts are allowed to separate ever so slightly, flash occurs and the tendency to part is increased. This spreading tendency is, however, taken up by the further extension of piston 30, sufliciently to prevent any flash from occurring. The thrust of piston 30 is preset by the use of conventional pressure regulation to adequately exceed the injection pressure thrust. After injection, and after a time interval for cooling the molding, the nozzle is withdrawn; but the clamping pressure may, though it need not, be relieved immediately after the injection stroke of the injection piston has been completed with the resultant release of separating pressure from the inside of the mold.

It is to be observed that the clamping pressure over the flat interfaces of the mold parts 18 and 19 tend to be uniform. This tendency is due to the employment of three thrust rods 46 and to the fact that the piston 30, being relatively thin, adjusts itself very slightly with respect to its own thrust axis so that the thrusts in the three thrust rods are equal and cause the platen 20 to rock slightly, for which its guides are sufficiently loose, so that the interfaces of the two die parts are substantially unrestrained frorn uniform interfacial contact. It is to be understood, of course, that the various parts are machined as accurately as possible to obtain the nearest possible uniformity of pressure without the automatic equalization provided by the piston 30 and thrust rods 46 and that the slight angular adjustment afforded by the piston absolutely insures the uniform distribution of contact pressure referred to. Accurate adjustment is further facilitated by threading rods 46 into sockets 48.

After the molding has cooled, pressure under piston 24 is maintained or restored, and the pressure under piston 30 is removed. Thus plate 40 is released and is rotated for registry of holes 42 with the upper ends of rods 46. The pressure under piston 24 is then released and pressure is applied to the upper side of piston 28 to cause lowering of the platen 20 and separation of the mold parts.

The sequence of operations as above recited is insured and certain safety functions are accomplished by a series of interlocking controls which will now be described insofar as the present invention adds to or modifies machines heretofore in use.

The apparatus comprises a conventional type of gate 56, which is, for clarity, illustrated apart from its normal position across access openings between strain rods 14 to the mold areas. The gate 56 controls three circuits. When gate 56 is fully closed, switches 62 and 64 are closed and the gate is latched closed by a solenoid released latch 66. Upon release of latch 66, the gate moves a short distance under the action of gravity or equal, to ward opening position, but remains sufliciently closed as to deny access of the operator to the forbidden areas. In this position the gate is stopped by a manually releasable catch 68. While so held by catch 68, switch 64 is open and switches 62 and '70 are closed. When the operator releases catch 68 to open the gate, switch 62 opensand switch 70 remains closed. The purposes of these switches will be pointed out hereinafter.

The apparatus further comprises the movable injector having the nozzle 50 which moves into contact with the nozzle seat 52 for injection purposes after the clamping has been effected by piston 30. The injector carries therewith a switch actuator arm 58 to which there is pivoted a switch actuating pawl 60. Pawl 60 closes switch 61 upon retraction of the injector (movement of nozzle 50 to the left in the drawing), the result of which activity will be recited and explained hereafter.

The platen 28 carries an arm 72 which engages a blocking disc drive control switch 74 when piston 24 reaches its maximum movement such as to permit free rotation of blocking disc 40.

Means are provided to rotate the blocking disc into and out of the blocking position. The means illustrated includes a cylinder 76 having one end pivotally mounted to pivot on a vertical axis, on a lug 78 carried on platen 20, the axis of the cylinder 76 being horizontal. A piston 80 having a piston rod 82 has one end pivoted to a pivot pin 83 secured to the blocking disc 40. The construction is such that the piston 80 in its movement in cylinder 76 produces the required rotation for blocking and releasing the thrust rods 46 with respect to platen 18 by means of the plate 40. The driving of piston 80 is eflected by fluid under pressure passing to one or the other of the two sides of piston 80 via flexible conduits 84 and via a solenoid actuated valve 86 to which there are connected a source of fluid under pressure and a conduit for allowing escape of fluid from either side of piston 80. As shown, energization of solenoid valve 86 upon closure of switch 74 is intended to move the piston 80 and plate 40 to blocking position. A clamping thrust control switch 88 is carried by platen 20 in a position to be closed by a finger 90, carried by plate 40, when the plate has moved to close the recess 58 against entry by thrust rods 46. Switch 88, upon closure energizes a solenoid 90a of a clamping thrust control valve 92 which admits high pressure hydraulic fluid into cylinder 32 and causes piston 30 to exert its clamping force on the dies through the rods 46, plate 40, and platen 20. Responsive to a source of hydraulic fluid under pressure 94, which is applied to piston 30 in effecting the clamping action, is a pressure responsive switch 96 which closes a circuit 98 when the pressure acting on the clamp suddenly rises due to the engagement of the mold parts with more than the required clamping thrust. Circuit 98 is associated with apparatus which changes the pressure producing pumping rate so as to maintain the required pressure, and the circuit also is associated with apparatus which upon closure of that circuit initiates, or conditions, apparatus for driving the injector nozzle and producing the injection, the pressure under piston 30 being maintained until the injection stroke of the injection piston has been effected. The apparatus and control of the injection phase are not described in detail here because they are a part of the prior art and are well known.

When injection has been completed, pressure is relived at nozzle 50 and it is retracted. This causes pawl 60 to close switch 61, thus releasing solenoid latch 66 and allowing a slight drop of gate 56 to be stopped by' manually releasable catch 68. This movement of gate 56 also opens switch 64 to deenergize solenoid 98a and closes switch 70 which energizes solenoid 90a and releases the hydraulic fluid from beneath piston 30 via valve 92. Clamping pressure is thereby removed from the mold, platen 20, and blocking plate 98. At this time the pressure under piston 26 remains or is reestablished so as to lift plate 40 from the top ends of thrust rods 46. Since the circuit through the solenoid valve 86 has been opened at switch 64, the solenoid valve 86 is reversed by spring 100 and causes piston 80 to move the blocking disc 46 to register holes 42 with recesses 50. The piston 24 remains up for some time for cooling the molded article so that ample time is allowed for the plate 40 to move to the non-blocking position. After sutficient time for cooling has been allowed, solenoid valve 102 is actuated to release fluid from below piston 24 and to apply separating pressure above piston 24. The platen 20 and related parts are thereby forced to the position shown in the drawing. Thereupon the operator releases gate catch 68 and the gate 56 opens thus disabling the timing controls for the injection apparatus proper.

The apparatus is adequate for molding articles of large area requiring large clamping thrusts Where the resulting articles does not tend to hold the mold closed with a great deal of tenacity.

Whereas I have shown and described a preferred embodiment of my invention, I wish it to be understood that there are modifications to the'invent-ion which will be apparent to those skilled in the art and which will fall within the scope and spirit of the invention. The scope of the invention, therefore, should be limited only by the scope of the hereinafter appended claims.

This application is a substitute application for my application, Serial No. 133,877 filed December 19, 1949 and now abandoned.

I claim:

1. An injection molding machine comprising, in combination, a stationary platen for holding a first mold part in a stationary position, a plurality of tie rods secured in parallelism to said stationary platen extending substantially beyond the position of the stationary mold part, a header secured to the tie rods to form, between the header and the stationary platen, a substantial space for the operation and occupancy of moving parts of the machine between a retracted position adjoining the header and a molding position adjoining the first platen, means providing a first cylinder and piston assembly in said space, means providing a second piston and cylinder assembly between said first assembly and said header, means for interconnecting said first named cylinder and piston assembly between said movable platen, and said second piston and cylinder assembly, said first named assembly having a relatively long stroke with a relatively small piston, said second assembly having a relatively short assembly is effective to apply a powerful mold closing force to said movable platen after advancement of said movable platen by said first named assembly, and a plurality of compression members carried by the piston of said second cylinder and piston assembly and abuttable, at the end of the stroke of said first assembly and upon application of said mold closing force, against said movable platen, thereby transmitting reactive pressure on said movable platen through said header, tie rods and stationary platen.

2. The structure of claim 1, wherein said header has a cylinder formed therein and a piston mounted in said cylinder to thereby form said second named cylinder and piston assembly.

3. The structure of claim 1, characterized by and including compression members in the form of a plurality of thrust rods carried by the piston of said second named cylinder and piston assembly and a plurality of passages in said movable platen to allow movement of the thrust rods therethrough.

4. The structure of claim 3, characterized by and including a locking plate carried by said movable platen and movable into and out of a position between said.

References Cited in the file of this patent UNITED STATES PATENTS Swenson Aug. 28, 1923 Roger Sept. 28, 1954 

